Apparatus for heat treatment of fine material

ABSTRACT

The apparatus comprises a rotary kiln, an intermediate chamber which is connected to the discharge end of the kiln and is arranged to receive fired material therefrom, and which extends a substantial distance below the discharge end of the kiln, so as to hold a column of substantial height of material discharged from the kiln, and apparatus for discharging air under pressure in a zone in the lower portion of a column of material in the chamber. A duct for conveying the material by air entrainment to a cooling zone, has its inlet in the zone in which the air is discharged in the lower portion of the column, and a conduit is provided for conducting to the rotary kiln air discharged from the cooling zone. The column of material in the chamber serves as a seal between the rotary kiln and the zone in which the air is discharged in the lower portion of the column.

United States Patent Graf-Galen-Strasse, Germany Feb. 12, 1969 Germany Priority APPARATUS FOR HEAT TREATMENT OF FINE MATERIAL 4 Claims, 1 Drawing Fig.

U.S. Cl 263/32, 34/57 A Int. Cl F27b 7/38 Field oiSearch 263/32 R; 34/57 R, 57 A References Cited UNITED STATES PATENTS 2,861,353 11/1958 Lellep 34/57A 3,203,681 8/1965 Rosa et al. 34/57 R Primary ExaminerJohn J. Camby Attorney-Marshall & Yeasting ABSTRACT: The apparatus comprises a rotary kiln, an intermediate chamber which is connected to the discharge end of the kiln and is arranged to receive fired material therefrom, and which extends a substantial distance below the discharge end of the kiln, so as to hold a column of substantial height of material discharged from the kiln, and apparatus for discharging air under pressure in a zone in the lower portion of a column of material in the chamber. A duct for conveying the material by air entrainment to a cooling zone, has its inlet in the zone in which the air is discharged in the lower portion of the column, and a conduit is provided for conducting to the rotary kiln air discharged from the cooling zone. The column of material in the chamber serves as a seal between the rotary kiln and the zone in which the air is discharged in the lower portion of the column.

APPARATUS FOR HEAT TREATMENT OF FINE MATERIAL The invention relates to an apparatus for heat treatment of fine material, with a rotary kiln, an intermediate chamber connected to the discharge end of the kiln for receiving the fired material, at least one cyclone separator connected to the intermediate chamber by a pneumatic conveying system, as well as a blower which passes a conveying airstream through the intermediate chamber and a cyclone separator and supplies the conveying air, thus preheated, as secondary air to the rotary kiln.

In the known apparatus of the class which has been described, the blower for drawing the stream of conveying air is arranged between the last cyclone separator and the secondary air duct which discharges into the rotary kiln. The fired fine material coming from the rotary kiln is directly conveyed pneumatically, without any intermediate chamber, to the cooling cyclone separators (using pressure or suction). In order to prevent undesired air form being drawn into the head of the kiln i .e. into thedischarge end of the kiln, on the one hand, a substantial negative pressure cannot' exist in the head of the kiln, and on the other hand, above all, no positive pressure can exist in the head of the kiln, because with positive pressure in the head of the kiln operation of the apparatus would become impossible. A properly operated rotary kiln, as is well known, should have in the head of the kiln a constant fluctuation between very slight positive pressure and very slight negative pressure, whereby an efficient operation of the entire rotary kiln installation is assured. For that reason, in the arrangements heretofore known the blower has been placed between the cooler and the rotary kiln. The principal disadvantage of this known arrangement is that the blower which is arranged on the hot air side is exposed to an undesirably high temperature, and at the same time is subjected to increased abrasion because of the content of fine material which has not been separated, in the air which is to be propelled by the blower. Accordingly, in order to protect the blower, a secondary air temperature can be maintained which is not as high as would be desired for optimal operation of the kiln and for good cooling of the fired fine material.

Moreover, by reason of sudden discharges of fine material from the kiln, which cannot always be prevented, the pneumatic conveying system for the cyclone separators and the cyclone separators themselves are subjected to fluctuating loads. This causes pressure fluctuations which affect the cooling operation in the cyclone separators.

In order to eliminate these serious defects in efficiency of heat transfer, one might consider locating the blower on the cold air side of the conveying air system, in which case it would of course be necessary to introduce the material by means of a chute or the like into the air-conveying system which is under positive pressure. Under these circumstances, however, there arises the difficulty of providing a seal between the head of the kiln and the cyclone separators, in order to prevent cold air from entering the kiln. The arrangement of an air lock or similar mechanical seal between the rotary kiln and the pneumatic conveying system is subject to the disadvantage of exposing such a seal to extremely great abrasion while it is at a high temperature.

Accordingly, the object of the invention is to eliminate the disadvantages which have been described by constructing an apparatus of this class in such a manner that, on the one hand, the blower is not subjected to high temperatures or to high abrasion even when a high secondary air temperature is maintained, and on the other hand the use of a mechanical seal at the outlet of the rotary kiln is eliminated. In accordance with the invention, this object is achieved in that the region in the intermediate chamber in which is located the connection with the pneumatic conveying system as well as a connection with a supply of air under pressure is sealed off from the kiln by a column of the material which has been discharged from the rotary kiln, and the exhaust gas conduit from the cyclone separators is directly connected with the rotary kiln.

In the apparatus of the present invention, the material is conveyed by air pressure from the intermediate chamber to the coding cyclone separators; the blower therefore is not subjected to a high temperature nor to abrasion by any residue of dust in the air. The necessary seal between the intennediate chamber which is supplied with air under pressure and the rotary kiln is provided in the apparatus of the present invention by the column of material discharged from the rotary kiln which is present in the upper part of the intennediate chamber. This eliminates the use of a special mechanical seal, as well as the severe abrasion to which such a device would be subjected at a high temperature.

Moreover, in case of a sudden discharge of fine material from the rotary kiln, there is less of a surge of material through the intermediate chamber to the cooling cyclone separators, and the supply of secondary air to the rotary kiln and the cooling of the fine material are more uniform.

These and other details of the invention are set forth in the following description of an embodiment which is illustrated in the drawing.

The drawing is a diagrammatic view of an apparatus embodying the invention.

To the rotary kiln 1, with its discharge casing 2, is con nected an intermediate chamber 3, into the bottom of which discharges a compressed air duct 5 which is supplied by a blower 4. The bottom of the intermediate chamber 3 can be provided with a porous false bottom 18 which is made for example of a ceramic material or a powdered metal material.

Also projecting into the intermediate chamber 3'is a conveying duct 6, the inlet opening 6a of which is arranged approximately above the nozzle 5a of the compressed air duct 5.

For cooling the fired fine material, there is provided a first cooling stage consisting of three cyclone separators 7, 8 and 9, as well as an after-cooling zone consisting for example of a whirling bed cooler 10. A blower 11 supplies to the cyclone separator 9, through a duct 12, a stream of cooling air, which then travels through a duct 13 to the cyclone separator 8, and from the latter through a duct 14 to the cyclone separator 7. Discharging into the duct 14 is the previously mentioned pneumatic conveying duct 6. The gas discharge duct 15 of the cyclone separator 7 leads into the discharge casing 2 of the rotary kiln 1.

The path of travel of the gases is indicated by arrows l6, and the path of the material is indicated by arrows 17. The operation of the apparatus is then as follows;

The fired fine material discharged from the rotary kiln 1 accumulates in the intermediate chamber 3 up to a predetermined column height. The stream of compressed air discharged into the intermediate chamber 3 by the blower 4 entrains the material present in the lowest portion of the intermediate chamber 3 and conveys it through the conveying duct 6 to the cyclone separator 7. The material travels through the material discharge pipe 17 of this cyclone separator 7 and through the duct 13 into the cyclone separator 8, then into the cyclone separator 9 and finally to the after-cooler 10. The cooling air supplied by the blower 11 travels in countercurrent to the material successively through the cyclone separators 9, 8 and 7 and then is supplied together with the conveying airstream from the conveying duct, through the duct 15, as secondary air to the rotary kiln 1.

In order to prevent the formation of bridges and incrustations in the intermediate chamber 3, agitating air can be injected through the porous false bottom 18 of the intermediate chamber 3, which can be supplied by a blower which is not shown in the drawing.

We claim:

1. Apparatus for heat treatment of fine material, comprising a rotary kiln, a duct for conveying to a cooling zone, by air entrainment, material which has been heat treated in the kiln, and a conduit for conducting to the rotary kiln air discharged from the cooling zone, wherein the improvement comprises an intermediate chamber which has its upper portion connected to the discharge end of the rotary kiln and is arranged to receive fired material therefrom, and apparatus for discharging air under pressure at a point in the lower portion of the intennediate chamber, the inlet of the duct for conveying material being located adjacent to such point, and the intermediate chamber being of such vertical length as to extend a substantial distance below the discharge end of the rotary kiln, so as to hold a column of substantial height of material discharged from the kiln, and being of such shape that the column of material in the chamber forms a seal between the rotary kiln and the zone in which air is discharged in the lower portion of the chamber.

2. Apparatus according to claim 1 wherein the inlet of the duct for conveying material by air entrainment is arranged approximately above the point at which air is discharged in the lower portion of the intermediate chamber.

3. Apparatus according to claim 1 wherein the cooling zone comprises a plurality of cyclone separators connected in series, and the duct for conveying material by entrainment discharges into a conduit connecting two cyclone separators.

4. Apparatus according to claim 1, wherein a porous false bottom is provided in the intermediate chamber. 

1. Apparatus for heat treatment of fine material, comprising a rotary kiln, a duct for conveying to a cooling zone, by air entrainment, material which has been heat treated in the kiln, and a conduit for conducting to the rotary kiln air discharged from the cooling zone, wherein the improvement comprises an intermediate chamber which has its upper portion connected to the discharge end of the rotary kiln and is arranged to receive fired material therefrom, and apparatus for discharging air under pressure at a point in the lower portion of the intermediate chamber, the inlet of the duct for conveying material being located adjacent to such point, and the intermediate chamber being of such vertical length as to extend a substantial distance below the discharge end of the rotary kiln, so as to hold a column of substantial height of material discharged from the kiln, and being of such shape that the column of material in the chamber forms a seal between the rotary kiln and the zone in which air is discharged in the lower portion of the chamber.
 2. Apparatus according to claim 1 wherein the inlet of the duct for conveying material by air entrainment is arranged approximately above the point at which air is discharged in the lower portion of the intermediate chamber.
 3. Apparatus according to claim 1 wherein the cooling zone comprises a plurality of cyclone separators connected in series, and the duct for conveying material by entrainment discharges into a conduit connecting two cyclone separators.
 4. Apparatus according to claim 1, wherein a porous false bottom is provided in the intermediate chamber. 